Since you have the fridge on that outlet I would pull a grounding wire in since you are concerned. As long as the ground comes from the same service panel your outlet is connected to this is legal and you would have a proper 3 wire outlet without the problematic tripping of a GFCI.
The ground can come from another circuit if you possibly have one in the area or back to the service panel.
Code recently changed and now allows a separate wire to be brought in as long as it is from the same service panel that the circuit originated in.